I currently cook with a wide mouth stainless steel water water bottle: https://mekineer.com/backpacking/kit...light-cookware
A collapsible stainless foil pouch would be lighter and easier to stow away when not needed. I guess the aluminum foil pouches *without* the plastic spouts could work as a dedicated cooking pot, but they would have to be pure steel with no layered plastic.
I value less pack volume just as much as less weight, hence collapsible.